This invention relates to compositions of the type which are rendered adhesive by the application of water and is particularly concerned with energy control sheets having a thin layer of such an adhesive bonded to one face thereof.
Energy control sheets, which are commonly used in conjunction with a window to inhibit passage of solar energy into a room, have been known for many years. Lion U.S. Pat. No. 2,774,021, for example, discloses a window shade in which a transparent or translucent self-supporting cellulosic foil is coated with a transparent-reflective layer of metal on the side adjacent the window, a protective layer of varnish or the like optionally being applied over the metal layer to reduce corrosion or mechanical damage.
A more sophisticated and efficient form of energy control film is shown in Antonson et al U.S. Pat. No. 3,290,203, which describes and claims a window unit in which a transparent polymeric foil is provided with a transparent-reflective metal layer on one face, the metal layer being protectively covered by a transparent protective layer which in turn is adhered to the inside of a conventional windowpane. The transparent protective layer may be either a coating or, if desired, a second self-supporting foil, as is shown in, e.g., Windorf U.S. Pat. No. 3,775,226.
Another form of energy control sheet is shown in copending Dahlen, Hansen and Weiher application Ser. No. 867,321, which discloses a product that not only excludes much of the undesired solar radiation from a room during summer months but also greatly reduces the transmission of near infra-red energy from inside the room to the outside during the winter months.
Still another form of energy control sheet, in which a polymeric substrate is consecutively coated with titanium suboxide, a transparent-reflective metal layer, and titanium suboxide is shown in Gillery U.S. Pat. No. 4,017,661.
Other forms of energy control film include the type in which a polyester foil is provided with a layer of dyed or pigmented copolyester resin, an adhesive typically being used to bond the copolyester layer to a windowpane.
Where energy control sheets are adhered to the inside of a windowpane, several types of adhesives have been employed. Water-soluble adhesives, such as are disclosed in the aforementioned Antonson et al patent, can either be applied to a windowpane in aqueous solution at the time of mounting the energy control sheet or, alternatively, pre-coated on the energy control film and dried, permitting reactivation at the time of mounting. An energy control sheet which has been adhered to a windowpane by means of such an adhesive can be removed after applying damp newspapers to the exposed surface, the moisture penetrating the backing and reducing the bonding properties of the adhesive. The existence of high humidity, condensation or frost over extended periods of time, however, often causes the sheet to pull irregularly away from the windowpane, creating water or air pockets which are sometimes known as "fingers" because of their appearance. The blending of silanes into some water-soluble adhesives substantially eliminates the "fingers" problem, but adhesion to the glass becomes so great that the sheet can be removed only by scraping with a razor blade.
The use of normally tacky and pressure-sensitive adhesives, which are normally not affected by moisture, overcomes the humidity-related problems described in the preceding paragraph. Adhesion is adequate but not so high that the sheet cannot be removed when desired. On the negative side, however, pressure-sensitive adhesives cannot conveniently be applied to a windowpane at the time an energy control sheet is to be installed; hence, the manufacturer of the sheet must supply the product pre-coated with adhesive. The tacky nature of such adhesives dictates that they be either provided with a temporary removable liner or protected with a detackifying water-soluble coating; see Theissen U.S. Pat. No. 3,681,179. Even so, application of large sheets coated with pressure-sensitive adhesive requires considerable care because of the adhesive's tendency to bond prematurely to the glass during the process of positioning and the difficulty in totally removing all air or liquid from between the adhesive and the glass after positioning. Additionally, it has been found difficult to provide a pressure-sensitive adhesive coating which has the optical clarity possessed by water-soluble adhesives.
Energy control sheets have also been held to windowpanes by means of one of the so-called "cling" vinyl adhesives, e.g., as disclosed in Willdorf U.S. Pat. No. 3,949,134 or Burger U.S. Pat. No. 4,095,013. While such adhesives also possess excellent moisture-resistance, they are intended for ready removability, permitting the sheets to be repeatedly removed and installed as desired. Consequently, they do not adhere so firmly to the windowpane as either of the other two adhesives previously discussed, a fact which may result in unintentional removal or vandalism caused by curious or destructive persons' picking at the energy control sheet.